Color under pressure: how multiple factors shape defensive coloration

Identifying the relative importance of different mechanisms responsible for the emergence and maintenance of phenotypic diversity can be challenging, as multiple selective pressures and stochastic events are involved in these processes. Therefore, testing how environmental conditions shape the distribution of phenotypes can offer important insights on local adaptation, divergence, and speciation. The red‐yellow Müllerian mimicry ring of Heliconius butterflies exhibits a wide diversity of color patterns across the Neotropics and is involved in multiple hybrid zones, making it a powerful system to investigate environmental drivers of phenotypic distributions. Using the distantly related Heliconius erato and Heliconius melpomene co‐mimics and a multiscale distribution approach, we investigated whether distinct phenotypes of these species are associated with different environmental conditions. We show that Heliconius red‐yellow phenotypic distribution is strongly driven by environmental gradients (especially thermal and precipitation variables), but that phenotype and environment associations vary with spatial scale. While co‐mimics are usually predicted to occur in similar environments at large spatial scales, patterns at local scales are not always consistent (i.e., different variables are best predictors of phenotypic occurrence in different locations) or congruent (i.e., co‐mimics show distinct associations with environment). We suggest that large‐scale analyses are important for identifying how environmental factors shape broad mimetic phenotypic distributions, but that local studies are essential to understand the context‐dependent biotic, abiotic, and historical mechanisms driving finer‐scale phenotypic transitions.

Section: Local Phenotypic Distributionsmentioning

confidence: 99%

Scale‐dependent environmental effects on phenotypic distributions inHeliconiusbutterflies

Martins

et al. 2022

“…The lack of association may be the result of disease playing a weaker selective role than expected, and the presence of other selection pressures within the environment. When multiple strong selection pressures are present within a given environment, the effect of one selective pressure may be minimized, altered, or obscured (Garcia et al, 2009 ; Postema et al, 2022 ; Sharma et al, 2020 ; Templeton & Shriner, 2004 ). Selection from the Metschnikowia epidemic was not the only selection pressure that Daphnia potentially faced during the time this data collection took place.…”

Section: Discussionmentioning

confidence: 99%

Partitioning variance in immune traits in a zooplankton host—Fungal parasite system

Westphal

Merrill

2022

Host immune traits arise from both genetic and environmental sources of variation. When immune traits have a strong genetic basis, the presence and severity of disease in a population may influence the distribution of those traits. Our study addressed how two immune‐related traits (gut penetrability and the hemocyte response) are shaped by genetic and environmental sources of variation, and how the presence of a virulent disease altered the relative frequency of these traits in natural populations. Daphnia dentifera hosts were sampled from five Indiana lakes between June and December 2017 before and during epidemics of their fungal pathogen, Metschnikowia bicuspidata . Collected Daphnia were experimentally exposed to Metschnikowia and assayed for their gut penetrability, hemocyte response, and multi‐locus genotype. Mixed‐effects models were constructed to partition variance in immune traits between genetic and environmental sources. We then isolated the genetic sources to produce genotype‐specific estimates of immune traits for each multi‐locus genotype. Finally, we assessed the relative frequency and dynamics of genotypes during epidemics and asked whether genotypes with more robust immune responses increased in frequency during epidemics. Although genotype was an important source of variation for both gut penetrability and the hemocyte response, environmental factors (e.g., resource availability, Metschnikowia prevalence, and co‐infection) still explained a large portion of observed variation, suggesting a high degree of flexibility in Daphnia immune traits. Additionally, no significant associations were detected between a genotype's immune traits and its frequency in a population. Our study highlights the power of variance partitioning in understanding the factors driving variation in Daphnia traits and motivates further research on immunological flexibility and the ecological drivers of immune variation.

“…Coloration is ubiquitous in nature and plays a significant role in animal communication, e.g., in the context of pollination, predator–prey interactions, or mating (Cuthill et al, 2017 ; Endler & Mappes, 2017 ; Postema et al, 2022 ). Colorful traits are often studied in the context of sexual selection where they are seen as handicaps that seem not to increase longevity or fecundity, so they are potentially not favored by natural selection.…”

Section: Introductionmentioning

confidence: 99%

Offspring plumage coloration as a condition‐dependent signal in the blue tit

García‐Campa

Müller

Morales

2023

In many species, offspring display conspicuous coloration already early in life, even though they might be very vulnerable to predation at this stage. However, most attention has been drawn to the conspicuous plumage displayed by adult individuals in a sexual context, while other signaling functions have been explored much less. Here, we investigated whether the yellow breast plumage of blue tit ( Cyanistes caeruleus ) nestlings shows patterns of condition dependence and hence signals individual quality, as has been described for adult birds. During three consecutive breeding seasons, we, therefore, explored the association between nestling body mass and three color components of the yellow breast plumage (i.e., UV chroma, carotenoid chroma, and total brightness), considering both within and among nest effects. Variation in carotenoid chroma was not related to body mass. However, UV chroma and total brightness varied with body mass on an among‐nest level, suggesting that they might signal aspects of genetic quality or parental rearing capacity. Interestingly, we also found a within‐nest effect of body mass on total brightness, suggesting that this is a good candidate for a condition‐dependent signal within the family. Thus, other family members could rely on brightness to adjust their behavioral strategies, such as feeding behavior in parents. Our study thus reveals that certain color components of the yellow breast plumage might signal different aspects of offspring quality, and they might have a correlated signaling value across life‐history stages.